1. Field of the Invention
The present invention relates to an electrophotographic image-forming device, and particularly to a tandem color laser printer for printing on a recording sheet and having a plurality of process cartridges arranged in a series along the direction in which the recording sheet is conveyed.
2. Description of the Related Art
Electrophotographic image-forming devices well known in the art form images on recording sheets, such as paper or transparencies, by transferring toner supplied from toner cartridges onto the recording sheet. In this type of image-forming device, part of the toner supplied from the toner cartridges may be deposited on an intermediate transfer belt and/or a conveying belt, and go unused.
When performing subsequent printing operations with toner deposited on the conveying belt, the toner on the conveying belt may transfer to the back surface of the recording sheet, forming unnecessary and unintended images on the recording sheet.
Japanese patent application publication No. 2005-266604 discloses an image-forming device having a cleaning device for removing toner from the conveying belt through electrostatic attraction. This image-forming device regulates a bias voltage applied to the cleaning device to a suitable voltage for cleaning during prescribed non-image forming periods, such as when the power of the image-forming device is turned on or when the image-forming device is restored from the sleep mode.
However, the optimum value of the bias voltage applied to the cleaning device is not constant, but varies according to the usage frequency of the image-forming device and ambient temperature and humidity. If a fixed bias voltage is applied as the optimum voltage, the image-forming device may not be able to remove toner sufficiently.
Therefore, an object of the present invention is to provide an image-forming device having a cleaning unit capable of reliably cleaning toner which has deposited on the conveying belt at all times through electrostatic attraction.